DESCRIPTION: Individuals addicted to illicit stimulants like cocaine play an important role in the continued transmission of HIV due to high rates of sexual risk behavior and, among those already infected, poor adherence to antiretroviral therapy. The field of neuroAIDS has provided convincing evidence that persons with HIV infection and/or drug addiction are more likely to experience deficits in decision making that are potentially relevant to HIV risk behavior. However, case-control designs and laboratory-based measures of decision making have been limited in predicting HIV risk behaviors in the real world. The goal of this Avenir Award is to advance our understanding of the cognitive mechanisms through which drug addiction and HIV infection impact decision- making processes relevant to HIV risk behavior. Specifically, this proposal addresses the following limitations of the field: (1) modeling addiction as a static condition rather than a chronic, relapsing disorder, with studies utilizing strict eligibility that minimize generalizability to the population and analyses that do not adequately account for variability and fluctuations in drug use; (2) cognitive assessments in controlled laboratory settings intended to optimize performance; and (3) reliance on convenience sampling for a hard-to-reach population. The proposed Avenir project will: use respondent driven sampling to engage a heterogeneous cohort of cocaine users, both HIV-positive and HIV-negative, from the community; conduct trimonthly laboratory-based assessments of neurobehavioral functioning over 1 year to capture natural fluctuations in drug use, decision making, and HIV risk behavior; and use mobile health (mHealth) technology to assess cognitive functioning and risk behaviors in real-time in natural settings. During an initial period of formative work, including focus group with the target population, we will adapt three widely used decision making tasks and develop an app for mobile devices. We will then screen and enroll 200 participants into the neuroAIDS cohort. Between the 3- and 6- month follow-ups, cohort participants will use a smartphone to record daily drug use and HIV risk behavior and complete ecological momentary assessments of decision making, drug state (e.g., craving, intoxication) and context (e.g., setting, social situation). This Avenir project builds logically from my previous research on decision making and HIV risk, integrating multi-disciplinary techniques to advance our understanding of HIV-related decision making in drug users. Through the use of innovative approaches to improve the